Thermal sensing detector cell for a computed tomography system and method of manufacturing same

ABSTRACT

The present invention provides a detector cell having an x-ray absorption component and a thermal sensing component configured to detect thermal differentials in the absorption component resulting from the absorption of x-rays. The absorption component comprises high density materials that respond thermally to the reception of x-rays or other HF electromagnetic energy. The thermal sensing component detects the changes in temperature of the absorption component and outputs electrical signals indicative of the number and intensity of the x-rays absorbed. An image reconstructor then processes those electrical signals to reconstruct an image of the subject scanned. A method of manufacturing the detector cell is also provided.

BACKGROUND OF THE INVENTION

The present invention relates generally to computed tomography imagingand, more particularly, to a detector cell for sensing thermal changesin response to the absorption of HF electromagnetic energy for use withcomputed tomography systems.

Typically, in computed tomography (CT) imaging systems, an x-ray sourceemits a fan-shaped beam towards a subject or object, such as a patientor a piece of luggage. Hereinafter the terms “subject” and “object”shall include anything capable of being imaged. The beam, after beingattenuated by the subject, impinges upon an array of radiationdetectors. The intensity of the attenuated beam radiation received atthe detector array is typically dependent upon the attenuation of thex-ray beam by the subject. Each detector element of the detector arrayproduces a separate electrical signal indicative of the attenuated beamreceived by each detector element. The electrical signals aretransmitted to a data processing system for analysis which ultimatelyresults in the formation of an image.

Generally, the x-ray source and the detector array are rotated about thegantry within an imaging plane and around the subject. X-ray sourcestypically include x-ray tubes, which emit the x-ray beam at a focalpoint. X-ray detectors typically include a collimator for collimatingx-ray beams received at the detector, a scintillator for convertingx-rays to light energy adjacent the collimator, and photodiodes forreceiving the light energy from the adjacent scintillator. Eachscintillator of a scintillator array converts x-rays to light energy.Each scintillator discharges light energy to a photodiode adjacentthereto. Each photodiode detects the light energy and generates acorresponding electrical signal. The outputs of the photodiodes are thentransmitted to a data processing system.

With these known scintillators, the scintillating component must be ofsufficient thickness to generate the requisite efficient x-raydetection. As a result, a minimum scintillating material thickness isnecessary for proper signal to noise generation by the photodiode. Theminimum requirements yield higher costs as well as limit the ability toreduce the overall detector cell size and spatial resolution of thedetector. Furthermore, detection inefficiencies in this two stepdetection process, x-rays to light and light to electrical signals, hasefficiency losses resulting in a diagnostic image of poorer quality orlower sensitivity.

High density materials may be advantageously used in a detection cell asthese materials may absorb HF electromagnetic energy in relatively thincross-sections. As a result, smaller detector cells can be fabricatedincreasing system resolution. Moreover, use of materials that change intemperature upon the absorption of HF electromagnetic energy allows foruse of thermal sensing components rather than photodiodes therebyproducing output signals more indicative of the HF electromagneticenergy detected resulting in a more sensitive and a diagnostic image ofgreater sensitivity.

It would therefore be desirable to design a detector cell for sensingthermal differentials in the detector cell resulting from the absorptionof HF electromagnetic energy thereby providing improved, higherresolution, and more sensitive detector signal output to a dataprocessing system of a CT system.

BRIEF DESCRIPTION OF INVENTION

The present invention is directed to a detector cell overcoming theaforementioned drawbacks that generates electrical signals indicative ofHF electromagnetic energy absorbed by the detector as defined by thermaldifferentials within the detector.

In accordance with one aspect of the present invention a CT detectorcell is provided and includes an HF electromagnetic energy absorptioncomponent comprised of a material configured to change in temperature inresponse to absorption of HF electromagnetic energy. The CT detectorcell further includes a thermal sensing component configured to detect achange in the temperature of the absorption component and output asignal indicative of the HF electromagnetic energy absorbed by the HFelectromagnetic energy absorption component.

In accordance with yet another aspect of the present invention, a CTsystem includes a rotatable gantry having an opening therein andconfigured to receive a subject to be scanned. The system also includesa subject positioner configured to place the subject to be scannedwithin the opening and an HF electromagnetic energy projection sourceconfigured to project HF electromagnetic energy toward the subject to bescanned. The system also includes an HF electromagnetic energy detectorarray having a plurality of detector cells which is configured to absorbHF electromagnetic energy passing through the subject to be scanned.Each detector cell includes a HF electromagnetic energy absorptioncomponent and a thermal sensing component. The CT system furtherincludes a data acquisition system (DAS) connected to the detector arrayand configured to receive electrical signals from each thermal sensingcomponent indicative of a change in temperature of a corresponding HFelectromagnetic energy absorption component. An image reconstructor isalso provided and connected to the DAS and configured to reconstruct animage of the subject from the electrical signals received by the DAS.

In accordance with a further aspect of the present invention, a methodof manufacturing a radiation detector sensor array for use with CTsystems includes the step of determining a high density material capableof changing in temperature upon absorption of radiation. The methodfurther includes forming an absorption array having a plurality ofabsorption cells from the high density material. The method alsoincludes coupling a thermal sensing array having a plurality of thermalsensing cells to the absorption array such that each thermal sensingcell corresponds to an absorption cell.

In accordance with yet another aspect of the present invention, adetector array for a CT system includes means for absorbing HFelectromagnetic energy and means for experiencing thermal differentialsin response to absorbed HF electromagnetic energy. The detector arrayalso includes means for detecting the thermal differentials as well asmeans for outputting a signal indicative of the HF electromagneticenergy absorbed as defined by detected thermal differentials.

Various other features, subjects and advantages of the present inventionwill be made apparent from the following detailed description and thedrawings.

BRIEF DESCRIPTION OF DRAWINGS

The drawings illustrate one preferred embodiment presently contemplatedfor carrying out the invention.

In the drawings:

FIG. 1 is a pictorial view of a CT imaging system.

FIG. 2 is a block schematic diagram of the system illustrated in FIG. 1.

FIG. 3 is a is a perspective view of one embodiment of a CT systemdetector array.

FIG. 4 is a is a perspective view of one embodiment of a detector.

FIG. 5 is a is illustrative of various configurations of the detector inFIG. 4 in a four-slice mode.

FIG. 6 is a cross-sectional view of one embodiment of the presentinvention.

FIG. 7 is a pictorial view of a CT system for use with a non-invasivepackage/luggage inspection system.

DETAILED DESCRIPTION

The operating environment of the present invention is described withrespect to a four-slice computed tomography (CT) system. However, itwill be appreciated by those skilled in the art of CT that the presentinvention is equally applicable for use with single-slice or othermulti-slice configurations. Moreover, the present invention will bedescribed with respect to the detection and conversion of x-rays.However, one skilled in the art will further appreciate that the presentinvention is equally applicable for the detection and conversion ofother HF electromagnetic energy. Further, the present invention will bedescribed with respect to a “third generation” CT system. However, thepresent invention is also applicable with first, second, and fourthgeneration CT systems.

Referring to FIGS. 1 and 2, a computed tomography (CT) imaging system 10is shown as including a gantry 12 representative of a “third generation”CT scanner. Gantry 12 has an x-ray source 14 that projects a beam ofradiation or x-rays 16 toward a detector array 18 on the opposite sideof the gantry 12. Detector array 18 is formed by a plurality ofdetectors 20 which together sense the projected x-rays that pass througha medical patient 22. Each detector 20 produces an electrical signalthat represents the intensity of an impinging x-ray beam and hence theattenuated beam as it passes through the patient 22. During a scan toacquire x-ray projection data, gantry 12 and the components mountedthereon rotate about a center of rotation 24.

Rotation of gantry 12 and the operation of x-ray source 14 are governedby a control mechanism 26 of CT system 10. Control mechanism 26 includesan x-ray controller 28 that provides power and timing signals to anx-ray source 14 and a gantry motor controller 30 that controls therotational speed and position of gantry 12. A data acquisition system(DAS) 32 in control mechanism 26 samples analog data from detectors 20and converts the data to digital signals for subsequent processing. Animage reconstructor 34 receives sampled and digitized x-ray data fromDAS 32 and performs high speed image reconstruction. The reconstructedimage is applied as an input to a computer 36 which stores the image ina mass storage device 38.

Computer 36 also receives commands and scanning parameters from anoperator via console 40 that has a keyboard or a like data entry module.An associated cathode ray tube display 42 allows the operator to observethe reconstructed image and other data from computer 36. The operatorsupplied commands and parameters are used by computer 36 to providecontrol signals and information to DAS 32, x-ray controller 28 andgantry motor controller 30. In addition, computer 36 operates a tablemotor controller 44 which controls a motorized table 46 to positionpatient 22 and gantry 12. Particularly, table 46 moves portions ofpatient 22 through a gantry opening 48.

As shown in FIGS. 3 and 4, detector array 18 includes a plurality ofdetectors 20. A collimator 15, as shown in FIG. 2, is positioned tocollimate x-ray beams 16 before such beams impinge upon detector array18.

In one embodiment, shown in FIG. 3, detector array 18 includes 57pixilated detectors 20, each detector 20 having a plurality of detectorcells 57 arranged in an array 56 with a size of 16×16. As a result,array 18 has 16 rows and 912 columns (16×57 detectors) which allows 16simultaneous slices of data to be collected with each rotation of gantry12. As will be described with particular reference to FIG. 6, eachdetector cell 57 includes an x-ray absorption component 59 and a thermalsensing component 60 that, in a preferred embodiment, is affixed to anundersurface of absorption component 59. Array 56 may have a pixilatedorientation or, alternatively, a columnar orientation.

Switch arrays 80 and 82, FIG. 4, include multi-dimensional semiconductorarrays coupled between detector array 18 and DAS 32. Switch arrays 80and 82 further include a plurality of field effect transistors (FET)(not shown) arranged as a multi-dimensional array. The FET arrayincludes a number of electrical leads connected to each of therespective detector cells 57 and a number of output leads electricallyconnected to DAS 32 via a flexible electrical interface 84.Particularly, about one-half of detector cell outputs are electricallyconnected to switch 80 with the other one-half of detector cell outputselectrically connected to switch 82. Each detector 20 is secured to adetector frame 77, FIG. 3, by mounting brackets 79.

Switch arrays 80 and 82 further include a decoder (not shown) thatenables, disables, or combines detector cell 57 outputs in accordancewith a desired number of slices and slice resolutions for each slice.Decoder, in one embodiment, is a decoder chip or an FET controller asknown in the art. Decoder includes a plurality of output and controllines coupled to switch arrays 80 and 82 and DAS 32. In one embodimentdefined as a 16 slice mode, decoder enables switch arrays 80 and 82 sothat all rows of the detector array 18 are activated, resulting in 16simultaneous slices of data for processing by DAS 32. Of course, manyother slice combinations are possible. For example, decoder may alsoselect from other slice modes, including one, two, and four-slice modes.

As shown in FIG. 5, by transmitting the appropriate decoderinstructions, switch arrays 80 and 82 can be configured in thefour-slice mode so that the data is collected from four slices of one ormore rows of detector array 18. Depending upon the specificconfiguration of switch arrays 80 and 82, various combinations ofdetector cells 20 can be enabled, disabled, or combined so that theslice thickness may consist of one, two, three, or four rows of detectorcells 20. Additional examples include, a single slice mode including oneslice with slices ranging from 1.25 mm thick to 20 mm thick, and atwo-slice mode including two slices with slices ranging from 1.25 mmthick to 10 mm thick. Additional modes beyond those described arecontemplated.

Referring now to FIG. 6, a cross-sectional view of a single detectorcell 57 is shown. As indicated previously, each detector cell 57includes an x-ray absorption component 59 as well as a thermal sensingcomponent 60. Absorption component 59 is positioned to detect x-rays 16or other HF electromagnetic energy waves passing through the subject tobe scanned, such as, a medical patient as illustrated in FIG. 1 .Preferably, absorption component 59 comprises a high density materialthat may absorb x-rays in a relatively thin cross-section. Such highdensity materials may include tungsten, lead, tantalum, or the like.Further, the high density materials should also have a “high z”characteristic or high atomic number. Furthermore, as will be discussedbelow, the materials used for the absorption component should also havelow heat or thermal capacity resulting in significant temperature changein response to x-ray absorption.

The high density, high z materials used to form the absorption component59 undergo detectable temperature change upon the absorption of x-raysor other HF electromagnetic energy. Several methods may be used toconstruct an array of absorption components including fabricating asheet of the selected material and then etching or laser cutting thesheet into pixilated structures. Alternatively, absorption component 59may also be formed by depositing the absorption materials in collimatorstructures, or in pixilated structures, or may also be sputtered orvapor deposited and then etched or laser cut. Masking operations mayalso be utilized to form an array of absorption components.

Still referring to FIG. 6, coupled to absorption component 59 is athermal sensing component 60. Thermal sensing component 60 is configuredto detect thermal differentials of absorption component 59 resultingfrom the absorption of x-rays 16. The temperature change of thematerials detected is proportional to the number and energy of thex-rays absorbed by component 59. Component 60 detects the thermal changeand outputs an electrical signal indicative of the absorbed x-rays. Thepresent invention contemplates several thermal sensing componentembodiments including a night vision infrared thermal sensor, a roomtemperature microbolometer, and other sensitive thermal measuringinstrumentation. It should be noted that the temperature change per CTview is an incremental temperature change with each view or increment intime. Therefore, the temperature difference of the detector from view toview must be calculated as a measure of the x-ray intensity absorbedduring that particular view.

The present invention may be incorporated into a CT medical imagingdevice similar to that shown in FIG. 1. Alternatively, however, thepresent invention may also be incorporated into a non-invasive packageor baggage inspection system, such as those used by postal inspectionand airport security systems.

Referring now to FIG. 7, package/baggage inspection system 100 includesa rotatable gantry 102 having an opening 104 therein through whichpackages or pieces of baggage may pass. The rotatable gantry 102 housesa HF electromagnetic energy source 106 as well as a detector assembly108 having detector arrays comprised of detectors similar to that shownin FIGS. 4 and 6. A conveyor system 110 is also provided and includes aconveyor belt 112 supported by structure 114 to automatically andcontinuously pass packages or baggage pieces 116 through opening 104 tobe scanned. Subjects 116 are fed through opening 104 by conveyor belt112, imaging data is then acquired, and the conveyor belt 112 removesthe packages 116 from opening 104 in a controlled and continuous manner.As a result, postal inspectors, baggage handlers, and other securitypersonnel may non-invasively inspect the contents of packages 116 forexplosives, knives, guns, contraband, etc.

As indicated previously, the present invention contemplates severalmethods to fabricate a detector cell as described above. In onepreferred embodiment, a thin sheet of absorption component materials isfabricated and immersed in a chemical etchant. After the sheet undergoesimmersion for a specific time, the sheet is transferred to a rinsestation that assists in removing acid located on the sheet surface. Oncethe acid is removed, the sheet is rinsed and dried. The chemical etchantfacilitates antistrophic etching of unprotected portions of the sheetwhich aids in the formation of absorption component.

In another preferred embodiment, plasma is applied to the sheet tofacilitate the forming of absorption component. To form component, thesheet is loaded into a chamber wherein pressure is reduced by a vacuumsystem. After the vacuum is established, the chamber is filled with areactive gas and a frequency field is created through electrodes in thechamber with the aid of a power supply. The frequency field energizesthe gas mixture to a plasma state. In the energized state, the gasmixture attacks unprotected portions of the sheet, and converts thesheet into volatile components which are subsequently removed by thevacuum system. When the volatile components are removed, an array ofabsorption components is formed within the sheet.

In a further embodiment, an array of absorption components may befabricated using ion beam milling techniques.

Therefore, in accordance with one embodiment of the present invention aCT detector cell is provided and includes a HF electromagnetic energyabsorption component comprised of a material configured to change intemperature in response to absorption of HF electromagnetic energy. TheCT detector cell further includes a thermal sensing component configuredto detect a change in the temperature of the absorption component andoutput a signal indicative of the HF electromagnetic energy absorbed bythe HF electromagnetic energy absorption component.

In accordance with yet another embodiment of the present invention, a CTsystem includes a rotatable gantry having an opening therein andconfigured to receive an subject to be scanned. The system also includesan subject positioner configured to place the subject to be scannedwithin the opening and a HF electromagnetic energy projection sourceconfigured to project HF electromagnetic energy toward the subject to bescanned. The system also includes a HF electromagnetic energy detectorarray having a plurality of detector cells which is configured to absorbHF electromagnetic energy passing through the subject to be scanned.Each detector cell includes a HF electromagnetic energy absorptioncomponent and a thermal sensing component. The CT system furtherincludes a DAS connected to the detector array and configured to receiveelectrical signals from each thermal sensing component indicative of achange in temperature of a corresponding HF electromagnetic energyabsorption component. An image reconstructor is also provided andconnected to the DAS and configured to reconstruct an image of thesubject from the electrical signals received by the DAS.

In accordance with a further embodiment of the present invention, amethod of manufacturing a radiation detector sensor array for use withCT systems includes the step of determining a high density materialcapable of changing in temperature upon absorption of radiation. Themethod further includes forming an absorption array having a pluralityof absorption cells from the high density material. The method alsoincludes coupling a thermal sensing array having a plurality of thermalsensing cells to the absorption array such that each thermal sensingcell corresponds to an absorption cell.

In accordance with yet another embodiment of the present invention, adetector ray for a CT system includes means for absorbing HFelectromagnetic energy and means for experiencing thermal differentialsin response to absorbed HF electromagnetic energy. The detector arrayalso includes means for detecting the thermal differentials as well asmeans for outputting a signal indicative of the HF electromagneticenergy absorbed based on the detected thermal differentials.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

What is claimed is:
 1. A CT detector cell comprising: a high frequency(HF) electromagnetic energy absorption component comprised of a materialconfigured to change in temperature in response to absorption of HFelectromagnetic energy; and a thermal sensing component configured todetect changes in temperature of the absorption component and output asignal indicative of the HF electromagnetic energy absorbed by the HFelectromagnetic energy absorption component based on the detectedchanges in temperature.
 2. The CT detector cell of claim 1 wherein thematerial includes at least one of tungsten, lead, and tantalum.
 3. TheCT detector cell of claim 1 wherein the thermal sensing component isaffixedly connected to the HF electromagnetic energy absorptioncomponent.
 4. The CT detector cell of claim 1 wherein the thermalsensing component includes one of an IR thermal sensor and amicrobolometer.
 5. The CT detector cell of claim 4 wherein themicrobolometer includes a room temperature microbolometer.
 6. The CTdetector cell of claim 1 incorporated as an array in at least one of amedical imaging device and a non-invasive package/baggage inspectiondevice.
 7. A CT system comprising; a rotatable gantry having an openingtherein and configured to receive an subject to be scanned; a subjectpositioner configured to place the subject to be scanned within theopening; an (HF) electromagnetic energy projection source configured toproject HF electromagnetic energy toward the subject to be scanned; anHF electromagnetic energy detector array having a plurality of detectorcells and configured to absorb HF electromagnetic energy passing throughthe subject to be scanned, wherein each detector cell includes; an HFelectromagnetic energy absorption component; and a thermal sensingcomponent; a data acquisition system (DAS) connected to the detectorarray and configured to receive electrical signals from each thermalsensing component indicative of a change in temperature of acorresponding HF electromagnetic energy absorption component; and animage reconstructor connected to the DAS and configured to reconstructan image of the subject from the electrical signals received by the DAS.8. The CT system of claim 7 incorporated into a medical diagnosticimaging device wherein the subject positioner includes a movable tableand the subject to be scanned includes a medical patient.
 9. The CTsystem of claim 7 incorporated into a non-invasive package/baggageinspection device wherein the subject positioner includes a conveyorapparatus and the subject to be scanned includes at least one of apackage and a piece of baggage.
 10. The CT system of claim 9incorporated into at least one of a postal inspection security systemand an airport security system.
 11. The CT system of claim 7 wherein theHF electromagnetic energy absorption component includes material thatundergoes a change in temperature In response to absorption of HFelectromagnetic energy.
 12. The CT system of claim 7 wherein the thermalsensing component includes one of a night vision IR thermal sensor and aroom temperature microbolometer.
 13. The CT system of claim 7 whereinthe HF electromagnetic energy detector array includes one of a pixilatedand a columnar orientation.
 14. The CT system of claim 7 furthercomprising a collimator to reduce HF electromagnetic energy scatter fromthe subject to be scanned.
 15. A detector array for a CT imaging system,the detector array comprising: means for absorbing high frequency (HF)electromagnetic energy; means for experiencing thermal differentials inresponse to absorbed HF electromagnetic energy; means for detecting thethermal differentials; and means for outputting a signal indicative ofthe HF electromagnetic energy absorbed based on the detected thermaldifferentials.
 16. A CT detector array comprising: a plurality of highfrequency (HF) electromagnetic energy absorption cells comprised of amaterial configured to change in temperature in response to absorptionof HF electromagnetic energy; and a plurality of thermal sensing cellsto sense changes in temperature of the plurality of HF electromagneticenergy absorption cells and output a signal indicative of the HFelectromagnetic energy absorbed by the HF electromagnetic energyabsorption component based on the change in temperature of the HFelectromagnetic energy absorption cells.
 17. The CT detector array ofclaim 16 wherein the plurality of HF electromagnetic energy absorptioncells comprises at least one of tungsten, lead, and tantalum.
 18. The CTdetector array of claim 16 incorporated into a CT imaging systemcomprising: a rotatable gantry having an opening therein and configuredto receive an subject to be scanned: a subject positioner configured toplace the subject to be scanned within the opening; a HF electromagneticenergy projection source configured to project HF electromagnetic energytoward the subject to be scanned; a data acquisition system (DAS)configured to receive electrical signals from each thermal sensing cell;and an image reconstructor connected to the DAS and configured toreconstruct an image of the subject from the electrical signals receivedby the DAS.
 19. The CT detector array of claim 16 wherein each thermalsensing cell includes one of a night vision IR thermal sensor and a roomtemperature microbolometer.